In preparing certain materials for analysis by a gas chromatograph, it is often necessary to mix them with a solvent. Unfortunately, however, when material prepared in this manner is injected into the stream of carrier gas entering a gas chromatographic column, the concentration of the solvent in the sampling gas eluting from the other end of the column is usually so great as to cause some types of detectors connected to the output of the column to malfunction, e.g., an atomic emission detector. Apparatus for permitting sample gas to flow through the detector during a detection mode and for diverting the portion of the flow of sample gas containing the solvent to a vent during a diversionary mode so as to prevent it from reaching the detector is described by Messrs. Scott A. Estes, Peter C. Uden and Ramon M. Barnes in an article entitled "High Resolution Gas Chromatography of Trialkyllead Chlorides with an Inert Solvent Venting Interface for Microwave Excited Helium Plasma Detection", published in Analytical Chemistry, Vol. 53, No. 9, August 1981. Since all of the components of the solvent dumping apparatus are on the inlet side of the detector, it has the following disadvantages:
(a) The large surface area that lies between the end of the chromatographic column and the inlet of the detector must be deactivated if polar or reactive materials are to be analyzed. PA1 (b) Unwanted peaks are produced in the output signals from the detector as a result of some solvent adsorbing on the relatively large surface area over which sample gas must flow during the diversionary mode and the subsequent removal of this adsorbed solvent by the make-up gas during the following detection mode. PA1 (c) It is difficult to maintain the pressure at the end of the chromatographic column the same during the detection and diversionary modes of operation for different rates of sample flow.